First use of VLBI to focus on a single star system for signs of life comes up empty

An antenna of the Goldstone Deep Space Communications Complex. Among other tasks, it has been used for VLBI. Image: NASA

(Phys.org) -- Astronomers in Australia have reported on their findings in their paper posted on the preprint server arXiv, regarding their use of Very Long Baseline Interferometry (VLBI) to study radio signals emitted from a single star system some 20 light years away. In their paper, soon to be published in the Astronomical Journal, the researchers say that the absence of signals from the studied star system was not unexpected as the odds of finding signals from intelligent beings when aiming at any given star system are not good when noting that there are billions to choose from. Despite this, they report feeling optimistic as the project proved that such technology could be used to rule out other star systems in the future.

Ruling out star systems is in some sense a matter of semantics, as the authors note. It could be that a planet inhabited by some form of life just isn’t broadcasting radio waves, or maybe is broadcasting but not at the frequency the team is looking at. They point out that had intelligent life forms light years away been looking at our planet just seventy years ago, they would have come up empty as well.

The paper documents the attempt by the Australian team (which is affiliated with the Search for Extra-Terrestrial Intelligence (SETI) project) back in 2007 to search for signs of life in a new way. Prior to this project, astronomers used radio telescopes that simply swept the sky looking for interesting signals. In this new approach the team focused on one star system which is thought to have two planets of the kind that might hold some form of life, using VLBI, which is where several telescopes are strung together virtually to create one large system. Such systems are better able to discern the difference between signals from other sources (such as our own satellites) versus ones that come from the source that is being studied. In all, the team detected 222 signals, all of which turned out to be from places other than Gliese 581, the star under study. They’re not disappointed however; they say their work proves very clearly that VLBI will make a fine tool for studying exoplanets that have been found in recent years by other teams using other technology, and because this search technique costs so little, they don’t see why it can’t be used to study every single possibility, until hopefully one day some team finds what the SETI group has been looking for all along. Definitive signs of intelligent extra-terrestrial life.

More information:
The First Very Long Baseline Interferometric SETI Experiment, arXiv:1205.6466v1 [astro-ph.IM]

AbstractThe first Search for Extra-Terrestrial Intelligence (SETI) conducted with Very Long Baseline Interferometry (VLBI) is presented. By consideration of the basic principles of interferometry, we show that VLBI is efficient at discriminating between SETI signals and human generated radio frequency interference (RFI). The target for this study was the star Gliese 581, thought to have two planets within its habitable zone. On 2007 June 19, Gliese 581 was observed for 8 hours at 1230-1544 with the Australian Long Baseline Array. The dataset was searched for signals appearing on all interferometer baselines above five times the noise limit. A total of 222 potential SETI signals were detected and by using automated data analysis techniques, were ruled out as originating from the Gliese 581 system. From our results we place an upper limit of 7 MW/Hz on the power output of any isotropic emitter located in the Gliese 581 system, within this frequency range. This study shows that VLBI is ideal for targeted SETI, including follow-up observations. The techniques presented are equally applicable to next-generation interferometers, such as the long baselines of the Square Kilometre Array (SKA).

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21 comments

Not bad for a first attempt. Now, if they could get the sensitivity high enough to pair their Bluetooth device at 20 light years, then they can rule it out... I suspect they'll have to add a few V's to VLBI before that's possible.

So, they appear to be saying that if someone (ET) was sending out a signal with a bandwidth of 1KHz (need bandwidth to transmit data) from twenty light years away, they would have to be transmitting with 7 Gigawatts of RF power.Since the transmitter efficiency is probably less than 70%, this would require the output of 10 of our nuclear power plants running continuously.What civilization would waste that much energy.We don't, we only listen.I can just imagine 100's of civilizations listening and none transmitting.By the way, none of our TV or radio stations transmit with enough power to be detected above the noise floor from that distance.Of course if we were transmitting directionally it would require far less power, but then which star do you pick to transmit to?

"By the way, none of our TV or radio stations transmit with enough power to be detected above the noise floor from that distance."

I find it reassuring that we are not making our presence known across too great a swath of space. We are not quite ready for visitors.

Agreed. It is natural for an alpha species to expand to its limits and to consume available resources. I have no comprehension how some can believe we are ready to face another alpha species when we can't even live with ourselves. When you have no viable ability to defend yourself the best chance to survive as a species may be to remain undetected.

Or make sure we are the first to make detection, then strike first. A first strike is the logical conclusion for whoever makes first discovery, if we find a civilization within reasonable range. The risk of the other side making the same decision is too great. It's too easy to hook engines onto a moderate sized asteroid for either side to take the chance that the other would not do it. Survival/fight-or-flight instincts are most likely a universal law of nature.

Only if we find life very far away can we assume any degree of safety. I would say that if we find intelligent life, the closer they are, the worse it would be.

Much safer to launch an asteroid with ion engines (or something similar) and get it going at 1/10th C or faster, and level everything on the planet. Twice. Then send people to examine what's left whenever we want.

Maybe the change in global temperature/spectrum is more a tell of our presents than any 'smart' waves we did send out.

What do you mean? Global warming? Looking at the Earth from space, you wouldn't see any measurable change. Keep in mind that our upper atmosphere has cooled, and that's what you see first from space. As for trace gases in the lower atmosphere, such as co2 or methane, that would also be very hard to measure from space. For example, we are still learning about the Martian atmosphere's composition and climate as we send probes to take on-site measurements. There's lots of things you can't see from a distance. It would also be hard to rule out natural causes, should any aliens happen to be looking at us.

I'm curious how much consideration amongst these SETI guys goes into the blocking of radio waves by astrophysical double layers. After all, our own ionosphere can block radio, according to day/night (etc). Double layers remain an active field of research, and we should not pretend that we understand everything about them at this point. It may turn out -- as Wal Thornhill has argued -- that life originates within the illuminated envelope of brown dwarf stars on planets which orbit within those diffuse stellar atmospheres. This is a great theory for the origin of life, because there would be no day or night, no seasons, a constant temperature and a supply of water raining down upon the planet's surface.

But, if such a claim was true, then perhaps a very strong double layer would stand in the way of that planet and the rest of the universe (?) ...

I'm betting you knew that was not going to be a popular suggestion. We have neighbors, lets piss them off?

We don't even have a viable way to defend ourselves from debris in "our" own solar system. Hitting a moving global target tens or hundreds of light years away while bobbing and weaving through an unknown number of tidal, gravitational, radiation and other forces of unknown and varying strengths and masses, well, good luck. ;)

Besides, we as a species haven't historically shown the ability to dedicate ourselves to a project of such magnitude. Also, one should be able to suppose that the society that was detected could have advanced significantly by the time a targetted asteroid got anywhere near them.

I'm still thinking it's best we stay hidden in the background noise if we are interested in survival.

So, they appear to be saying that if someone (ET) was sending out a signal with a bandwidth of 1KHz (need bandwidth to transmit data) from twenty light years away, they would have to be transmitting with 7 Gigawatts of RF power.Since the transmitter efficiency is probably less than 70%, this would require the output of 10 of our nuclear power plants running continuously.What civilization would waste that much energy.We don't, we only listen.

We transmit far more than that, only not at those frequencies. Consider how much we emit at the sodium doublet wavelength from street lighting:

I'm betting you knew that was not going to be a popular suggestion. We have neighbors, lets piss them off?

Yeah, I don't like it either, but it does make some sense.

The only reasonable argument for making peaceful contact would be fear of reprisal if our first strike failes somehow. For example, as you suggested, we could miss the target. Or, perhaps the world we encounter doesn't stand alone. Or, perhaps they are already watching us closely and we don't know it. The debate over how to react if we ever do find intelligent life would be interesting.

I would personally suggest a multi-pronged solution, with multiple fall-back options. Perhaps watch them quietly for a time, while establishing a lifeboat colony on Luna and/or Mars. Also perhaps launch robot probes while building a human mission spacecraft and an asteroid weapon system. Then, when everything is in place, we contact them via radio signals? One thing's certain; words are like arrows.

What if we detect someone, 40 LY distant for example, we try to contact them, wait 80, 90, 100 years and still no answer? Did they hear us? Did they answer and we missed it? Is there an asteroid weapon on its way to us, already half way here? At what point do we finally let our survival be the priority and stike out at them before it's too late?

What if they came to the same conclusion and our weapons pass each other in space, leaving us both extinct? In the vastness of time and space, what are the chances that such a scenario hasn't already happened?

Mutually assured destruction works to discourage terrestrial nuclear war. Extraterrestrial war would work in the opposite direction, where it would be something more like "exclusive assured survival". If you fear global warming, an alien race should dwarf that fear.

At what point do we finally let our survival be the priority and stike out at them before it's too late?... If you fear global warming, an alien race should dwarf that fear.

The advice is "think before posting".

The galaxy has existed for about 10 billion years, and for 5 billion before the Sun formed. If there is even a single other race out there, they will have been in space for several billion years. Current technology (e.g. based on Ikaros) is probably capable of launched a solar sail to nearby stars at 1% of the speed of light, that's just 400 years to Alpha Centauri, and 10 million years to create a network with a communications node around every star in the galaxy.

If there is another technological race out there, they have been watching our planet evolve since before the dinosaurs and have allowed that to happen. If they wanted us extinct, we wouldn't be here.

More seriously; we have no reason to conclude that life elsewhere follows a different pattern than what is and always has been natural here on earth. The strong prey on the weak. An alpha species rises to the top of its food chain and consumes what resources are available. Intelligence != xeno-compassion. I know brilliant people who are afraid of rats, spiders and snakes, and if able would kill them in an instant. What if "we" are the pests, how safe would we be?

More seriously; we have no reason to conclude that life elsewhere follows a different pattern than what is and always has been natural here on earth. The strong prey on the weak. An alpha species rises to the top of its food chain and consumes what resources are available. Intelligence != xeno-compassion. I know brilliant people who are afraid of rats, spiders and snakes, and if able would kill them in an instant. What if "we" are the pests, how safe would we be?

Perhaps the only way to possess extreme amounts of technology is to develop extreme benevolence. I'd like to think this is the universes closed loop feedback system. Species who are too violent destroy themselves with their technology before it is advanced enough to affect other planets and civilizations. I don't think an alpha-mentality species would survive themselves.

More seriously; we have no reason to conclude that life elsewhere follows a different pattern than what is and always has been natural here on earth.

Our present society is unlikely to last for billions of years, it must change to survive.

What if "we" are the pests, how safe would we be?

If we were considered "pests", we would have been eradicated. The fact is that we haven't.

Species who are too violent destroy themselves with their technology before it is advanced enough to affect other planets and civilizations. I don't think an alpha-mentality species would survive themselves.

That may be true but we already have most of the technology needed to launch an interstellar probe and the remainder is in the labs. We may not survive long term but a fire-and-forget mission to build a comms network using automated self-replicating probes would go on without us.

What is the ratio of the energy that star Gliese 581 generates compared to the energy that we receive from it, which is represented by that pinpoint of light? So, how much of the energy of a 50,000 watt radio transmitter (too powerful to be legal in the U.S., but not in Mexico) on Gliese 581E actually reaches us, then? The answer is none, or an undetectable, negligible amount. You need a transmitter the size of the south pole of Saturn using all of the energy that can be harvested from that planet to send detectable information to Gliese 581E. Humans are so naive.

Or make sure we are the first to make detection, then strike first. A first strike is the logical conclusion for whoever makes first discovery, if we find a civilization within reasonable range. The risk of the other side making the same decision is too great -SwiftTard

Your mask of measured respectability is slipping. Why don't you go back to your wedge policy of questioning the minutiae of climate change science/papers?

Or make sure we are the first to make detection, then strike first. A first strike is the logical conclusion for whoever makes first discovery, if we find a civilization within reasonable range. The risk of the other side making the same decision is too great -SwiftTard

Your mask of measured respectability is slipping. Why don't you go back to your wedge policy of questioning the minutiae of climate change science/papers?

There should be no issue with discussing alternate opinions or theories. If we all thought the same or even just agreed with each other, then what would be the point?

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